Multiple molecules exist on the surface of lymphocytes that are important for development, activation and regulation of the immune response. Of prime importance in this regard is the clonotypic alpha beta heterodimer T cell receptor (TCR) that is noncovalently associated with the multicomponent T3 complex. In order to study the expression of the TCR-T3 complex, rabbit anti-peptide antibodies specific for human TCR alpha and beta chains and T3 delta-chains were prepared. With these reagents, it was possible to show that all of the alpha, beta and CD3 chains present on the surface of lymphocytes are bound as a TCR-CD3 complex and that the two beta chain isotypes (C beta 1 and C beta 2) were expressed in about equal amounts. In the mouse an anti-peptide antibody was used to define a completely new TCR- T3 complex. This was initially described on Lyt2-, L3T4- thymocytes and were found to consist of a 35 Kd gamma chain disulfide linked to a 45 Kd delta chain. This receptor is expressed prior to the alpha beta TCR in the developing thymus and appears to be representative of a distinct T cell lineage differentiating within the thymus. Additional studies detected this receptor on a novel population of Thy-1+, T3+, Ia- dendritic epidermal cells (DEC). At least 60% of these cells were positive upon in situ staining with the anti-gamma chain antibody. Cell lines derived from DEC were found to express three types of novel TCRs: "classical" gamm-delta of 35 Kd and 45 Kd respectively, an apparent gamma-gamma homodimer and an as yet undescribed receptor that may contain C gamma 4 protein. Hybridomas that express these receptors and that can be grown in large amounts are being used to analyze the structural and functional properties of these receptors. In addition to the TCR-T3 complexes, there are other cell surface molecules that appear to play a role in T lymphocyte signal transduction. One such molecule, TAP a Ly-6 linked T-cell activating glycoprotein has been characterized and has been found to be similar, but distinct, from the Ly6.1E antigen.